Method and apparatus for oxidizing organic matter

ABSTRACT

Method and apparatus for biologically oxidizing organic matter. Finely powdered organic matter is suplied into the top end of an upright, high reaction vessel ( 1 ). The vessel ( 1 ) has been filled up substantially completely by small balls, on the surfaces of which the matter to be oxidized is present in thin layers. By means of a conveyor ( 6 ) outside the vessel, the balls are transferred uppwards, whereby the balls in the reaction vessel ( 1 ) flow downwrds. Oxidizing air is blown uppwrds against the flow of balls, whereby in the upper section of the vessel, drying takes place in the first instance and then is formed an oxidizing zone automatically by microbial activity in a section, wherein the best oxidizing conditions are prevailing. Exhaust air is cleaned by means of ionic cleaners ( 14 ) and singlet oxygen generators ( 27 ) and oxidized matter is recovered from the bottom end of the reaction vessel.

[0001] The invention relates to a method for biologically oxidizing organic matter. The method comprises oxidizing organic matter in a reaction vessel, which is supplied with air regulated in terms of heat and humidity and from which is discharged a hot moist gas. For enhanced oxidation, the organic matter is provided with a recyclable oxidizing surface. The organic matter comprises typically fluidized finely powdered waste.

[0002] The invention relates also to an apparatus for oxidizing organic matter while the organic matter is in the state of finely powdered waste, said apparatus comprising a reaction vessel, devices for supplying matter to be oxidized into the reaction vessel, devices for circulating an oxidizing surface in the reaction vessel, devices for separating oxidized matter from the circulated oxidizing surface and from biologically unoxidized matter, devices for supplying the reaction vessel with air regulated in terms of heat and humidity, devices for drawing a hot moist exhaust gas from the reaction vessel, devices for scrubbing the exhaust gas, and a heat recovery unit for the transmission of heat from the exhaust gas to the inlet air.

[0003] Organic matter is supplied at the top end of a reaction vessel and a valuable final product, useful e.g. as a soil conditioner, is obtained from the bottom end of the reaction vessel. In the reaction vessel, high-temperature micro-organisms use the organic matter for nutrition. When growing and multiplying, the microbes demand nutrition and enormous amounts of oxygen. At the same time, they produce thermal energy, water, carbon dioxide, and useful biomass.

[0004] When the organic matter has a dry content (ka) which is low, e.g. in organic sludges ka<20%, it will be problematic to provide oxidation sufficiently effective for such a microbial activity which is required for a total oxidation of the organic matter. This problem has been addressed by adding various builders in the sludge mass, such as wood chips, peat, etc., but the constitution and composition of such prior known builders do not provide an optimal oxidation performance.

[0005] The invention concerns a method and apparatus capable of maximizing the oxidation performance of a biological oxidation process, i.e. the oxygen supply of microbes, so as to speed up the entire oxidation process, to oxidize all of the organic matter, and to provide a substantial increase in production capacity more economically than in the prior known methods.

[0006] This objective is accomplished by a method as set forth in the appended claim 1 and by an apparatus as set forth in claim 4. The non-independent claims disclose preferred embodiments of the invention.

[0007] One embodiment of the invention will now be described in more detail with reference to the accompanying drawing, showing an apparatus of the invention in a schematic vertical section.

[0008] A thermally insulated reaction vessel 1 comprises an upright cylinder, having a height which exceeds its diameter. In the middle of the cylinder 1 is a rotatable shaft 2, driven by a motor 3 at a variable speed through the intermediary of a reduction gear 4. A manifold or distributor plate 9, consisting of pipe rings and radial tubular members interconnecting the same, disperses organic matter evenly across the vessel 1 in its top end. The organic matter is delivered by means of a pipe 8 into the manifold or plate 9. The organic matter may comprise e.g. sludge from a sewage treatment plant, liquid porcine manure or other agricultural liquid manure or other organic waste. The dry content of organic matter to be treated with the apparatus is typically 1-30%, whereby it is generally in a fluid state when ka<15%. When ka>15%, it may be beneficial to elutriate the matter in water prior to oxidation. Dry waste can also be milled to a finely powdered form and elutriated in water for bringing the waste to a fluid state and for facilitating separation of the unoxidized portion from the oxidized product and the oxidizing surface.

[0009] The vessel 1 is filled with substantially round bodies, e.g. spheres 7, of an essentially totally unoxidizable material, having a diameter within the range of 1-5 cm, most preferably about 2-3 cm, and having their surface treated in such a way that the organic matter is highly adhesive to the spherical surface. If the organic matter is excessively dry, it is possible to add water therein through a mixer 35 for making it adhere to the surface of the spheres 7 in the form of a thin layer. It is an objective that the spherical surface be provided with such a thin layer of oxidizable matter that the oxygen obtained from regulated air penetrates the layer of material on the spherical surface. The layer of material has a thickness which is typically less than 2 mm.

[0010] The shaft 2 is fitted with vane-like stirring elements 5, extending towards a wall of the reaction vessel 1. Spheres are carried by a conveyor 6 from the bottom to the top of the reaction vessel 1. A result of this is, of course, that within the vessel 1 is a flow of spheres which is directed downwards. As the spheres are generally lighter than the matter to be oxidized, having e.g. a specific weight of about 0.5 kg/dm³ or less, the spheres, which are coated with a substance having a density higher than that of the spheres, strive to descend faster than cleaner spheres, with the result that substantially all the spheres receive a coating from the matter to be oxidized. The spheres 7 are returned by way of a cover of the vessel 1 and the matter to be oxidized is passed therebelow for precluding the formation of aerosols.

[0011] Regulated oxidation air is blown into the reaction vessel 1, generally from below its middle section. Therefor, the reaction vessel 1 has its inner wall fitted with a pipe frame 12, including orifices and having air supplied therein by means of a pump 17 through a duct 18, typically from a heat recovery unit 16. The pipe frame 12 comprises e.g. annular and radial pipes. The pipe frame 12 has its vertical position preferably adjustable. The adjustment can be implemented by a vertical adjustment of hangers placed within the vessel 1.

[0012] The reaction vessel 1 can have its height adjustable by adding or removing cylindrical blocks 1 a, which can be placed on top of each other for assembling the reaction vessel like a lego tower.

[0013] The discharge of air from the bottom end of the vessel is precluded, e.g. in such a way that a receiving space 21 for oxidized matter has a bottom 23, which is otherwise solid except for a gap 24 connecting the space 21 with a conveyor 25 which can be connected, if necessary, by way of a shut-off feeder 33 with another conveyor 34 for delivering a finished product into a container 26. Thus, the air is forced to flow in the reaction vessel 1 up towards the top end of the reaction vessel. The reaction vessel has its top end provided with an exhaust fan 15 for drawing out the air fed inside the reaction vessel and for guiding it out through an air cleaner 14 and the heat recovery unit 16 and an air cleaner 27. The spheres 7 constitute a dense homogeneous system of flow channels distributed all over the reaction vessel 1, having in association therewith a large surface area of the substance to be oxidized. At the mid-height section of the reaction vessel is established a so-called oxidizing zone, wherein moisture and oxygen conditions, as well as temperature, are appropriate for microbial activity. The oxidizing microbial activity will be particularly effective as the entire amount of air proceeds continuously through the entire oxidizing zone and the material to be oxidized. The air heated in biological oxidation and the dry hot air supplied, if necessary, into the vessel's top section are capable of drying the material in the vessel's top section, such that it has been appropriately dried by the time it reaches the oxidizing zone, which self-establishes itself always in a given region between an air supply point 12 and the reaction vessel's top end. The residence or dwell time of a material to be oxidized is regulated by means of the sphere conveyor 6 and the reaction vessel's top end is supplied with just enough material to provide a suitable material layer on the spherical surface. Regulation parameters include also a flow rate of air, its temperature and humidity.

[0014] Reference numeral 14 designates a discharge air cleaner. In practice, the discharge or exhaust air can be cleaned most preferably by means of ionic cleaners 14 and singlet oxygen generators 27 (patent application FI 20020304). The discharge air can be cleaned with ionic cleaners which are known per se, e.g. from publications EP-1178860 and EP-1165241. Operation of the ionic cleaner or ionizing particle separator 14 is based on charging the particles present in the air flowing through a void separator chamber, and on collecting the charged particles by means of an electric field onto grounded or live collecting surfaces, from which the particles are flushed with water and the flushing water is most preferably recycled back to the oxidizing process and discharged through a heat exchanger 16 as condensation water. The number of ionic cleaners 14 is typically two or more (just 1 is shown), and the air flow therebetween travels in a multitude of ionic blowpipes, which are fitted with the singlet oxygen generator 27. The Applicant's patent application FI 20020304 discloses an example of the suitable ionic cleaner 14 and the singlet oxygen generator 27. In the present case, the singlet oxygen generator 27 is positioned downstream of the heat exchanger 16, which may also be provided with a separate condenser for the condensation of water vapour. The singlet oxygen generator 27 comprises an electrically conductive electrode inside a glass tube, and outside the glass tube is a spiral electrode inside a dielectric. Between the ends of these electrodes is coupled a high-frequency source of high voltage. The tube and the electrodes are housed in a jacket tube, through which air is blown by means of a fan, said air entraining singlet oxygen which is produced by a corona effect breaking up oxygen molecules of the flowing air, said corona effect being created by the spiral electrode.

[0015] The fan 15 expels the refined gases through the heat exchanger 16, and the fan 17 delivers dry clean atmospheric air, which has been heated in a regulated fashion in the heat exchanger 16, through the duct 18 into the reaction vessel 1 and/or through a separate heater 28 and a distributor 29 into the top section of the reaction vessel 1. If blow drying for the top section is not needed, it can be shut off by means of a control valve 30.

[0016] In major facilities, it is preferred that a common air treatment unit be built for a plurality of reaction vessels 1.

[0017] The reaction vessel 1 is provided with a perforated floor 20, which has a hole size substantially smaller than the diameter of the spheres 7 and below which is the receiving space 21 for oxidized matter. A scraper blade 19 driven by the shaft 2 scrapes the perforated floor 20, pushes the oxidized powdered product through the holes, and prevents blocking of the floor holes and simultaneously advances spheres by way of a shut-off feeder 32 onto the conveyor 6. Thus, the perforated floor 20 constitutes a screen, above which occurs effective mixing by means of the scraper 19 and the stirring vanes 5, in order to effect stripping of the oxidized matter from the spheres 7. Hence, between the floor 20 and the blowpipe system 12 is established a stripping zone, in which the stirring vanes 5 have their blades arranged more densely than elsewhere above the pipe system 12.

[0018] The spheres 7 are preferably made of a homogeneous material, whereby, while wearing, said spheres develop continuously the same effective gripping surface which is highly adhesive for the material. Although the bodies 7 have preferably the shape of a sphere and in this context are referred to as “spheres”, it should be understood that these may comprise bodies of other shapes or materials with a high surface area to volume ratio.

[0019] The invention is not limited to the above-described embodiment as its structural details may involve a multitude of variations. For example, the sphere conveyor 6 can be built inside the vessel 1 as a lifting screw. The stirring elements 5 are not necessarily mobile but, instead, may comprise stationary guides.

[0020] The reaction vessel 1 can be supplied not only with sludge, but also with dry waste, as long as it has been comminuted beforehand. Humidity control is carried out by condensation water 16 w, and by flushing water 14 w for the ionic fans 14, which is always recycled back to circulation.

[0021] Waste materials can be pre-aerated and, if necessary, sludges can be adjusted to such an acidic pH that ammonia does not evaporate and cause losses of N in fertilizer production.

[0022] Even debris-containing biowaste can be oxidized by setting a screen 31 upstream of the sphere conveyor 6 for the removal of debris. Thus, the apparatus is applicable as a general purpose oxidizer for all sorts of organic matter. The apparatus can be constructed to be very compact or very large.

[0023] The function of the shut-off feeders 32 and 33 is to preclude the outflow of air from the reaction vessel 1 anywhere else except from the top by means of the exhaust fan 15.

[0024] The reaction vessel 1 and all pipes, conveyors and other equipment are thermally insulated. 

1. A method for biologically oxidizing organic matter while the organic mater is in the state of finely powdered waste, said method comprising the oxidation of organic matter in a reaction vessel (1), which is supplied with oxidizing air regulated in terms of heat and humidity and from which is discharged a hot moist gas, and for enhanced oxidation, the organic matter is provided with a recyclable oxidizing surface, characterized in that the waste is supplied into the top end of the upright reaction vessel (1), that in the reaction vessel is effected stirring and/or migration of spheres (7), which essentially fill up the reaction vessel and on the surfaces of which the matter to be oxidized is present in thin layers, that oxidizing air is blown into the reaction vessel below the reaction vessel's oxidizing zone and, if necessary, into and/or above the oxidizing zone, that the discharge of air from the bottom end of the reaction vessel is precluded and air is discharged from the top end of the reaction vessel by the application of suction, exhaust air is cleaned, heat is transferred from the exhaust air to the air being blown into the reaction vessel, and oxidized matter is discharged from the bottom end of the reaction vessel.
 2. A method as set forth in claim 1, characterized in that the spheres (7) are migrated from the bottom end to the top end of the reaction vessel (1), whereby the reaction vessel develops a downward flow of spheres.
 3. A method as set forth in claim 1 or 2, characterized in that exhaust air is cleaned by means of ionic cleaners (14) and/or singlet oxygen generators (27).
 4. An apparatus for oxidizing organic matter while the organic matter is in the state of finely powdered waste, said apparatus comprising a reaction vessel (1), devices (8, 9) for supplying the reaction vessel with matter to be oxidized, devices (12) for supplying the reaction vessel with oxidizing air regulated in terms of heat and humidity, devices (13, 15) for drawing a hot moist exhaust gas from the reaction vessel, devices (14) for scrubbing the exhaust gas, and a heat recovery unit (16) for the transmission of heat from the exhaust gas to the inlet air, characterized in that the reaction vessel (1) comprises an upright vessel higher than its diameter, the top end of which is provided with distributing elements (9) for matter to be oxidized for dispersing the matter to be oxidized across the reaction vessel (1) in its top end, that the oxidizing surface is constituted by biologically unoxidizable spheres (7), which essentially fill up the reaction vessel and on the surface of which the matter to be oxidized deposits in a thin layer, and that the apparatus further comprises elements (5) for stirring and/or migrating the spheres (7) in the reaction vessel (1), elements (6) for conveying the spheres (7) from the bottom end to the top end of the reaction vessel, elements (12, 29) for blowing oxidizing air into the reaction vessel below its oxidizing zone and, if necessary, into and/or above the oxidizing zone, shut-off elements (23, 32, 33) for precluding the discharge of oxidizing air from anywhere else except from the top end of the reaction vessel (1), elements (13, 15) for exhausting hot humid air from the top end of the reaction vessel, and elements (14, 27) for cleaning the exhaust air.
 5. An apparatus as set forth in claim 4, characterized in that the reaction vessel (1) is cylindrical and in the middle of the vessel is a controllably rotatable shaft (2), the elements (5) for stirring and/or migrating the spheres being attached thereto.
 6. An apparatus as set forth in claim 5, characterized in that the blowing elements (12) for oxidizing air comprise a pipe frame, which is provided with orifices and which is supplied with air.
 7. An apparatus as set forth in claim 4, characterized in that outside the reaction vessel (1) is a conveyor (6) for carrying the spheres from the bottom end to the top end of the reaction vessel (1) at the same time as the spheres descend gravitationally downward in the reaction vessel (1), in which the oxidizing air flows upwards.
 8. An apparatus as set forth in any of claims 4-7, characterized in that the reaction vessel (1) is provided with a perforated floor (20), which has a hole size smaller than the diameter of the spheres (7) and below which is a receiving space (21) for oxidized matter, and that on top of the floor (20) is a scraper (19).
 9. An apparatus as set forth in claim 8, characterized in that the elements (12) for blowing the oxidizing air are located above the floor (20), at a vertical distance therefrom.
 10. An apparatus as set forth in any of claims 4-9, characterized in that the receiving space (21) for oxidized matter has its bottom (23) provided with a gap (24), whereby the receiving space (21) is in communication with a discharge conveyor (25), and that on top of the bottom (23) is a scraper (22).
 11. An apparatus as set forth in any of claims 4-10, characterized in that the bodies (7) or a material, functioning as an oxidizing surface, are separated from unoxidized matter (debris) by means of a screen (31) prior to returning the bodies to the top end of the reaction vessel (1).
 12. An apparatus as set forth in any of claims 4-11, characterized in that the cleaning elements for exhaust air include an ionic cleaner (14) and/or a singlet oxygen generator (27). 